Flexible shafts comprise basic elements of power transmission and are designed to transmit power or control from a driving element to an element to be driven. Transmission may be over, under, or around obstacles or objects where transmission by solid shafts would be impractical or impossible.
In a typical rotatable flexible shaft, a wire mandrel has a plurality of layers of closely coiled wire wound thereover, each of the layers being successively wound over another in alternately opposing directions, i.e., right or left-hand lay. This shaft is usually covered by a flexible casing, metallic or covered, and a clearance between the shaft and casing is provided in order that the shaft may rotate freely within the casing.
Rotatable flexible shafts are of two basic types--power driven and remotely controlled. Power driven flexible shafts are designed primarily for motor-driven or high speed operation in one direction. Remote control flexible shafts, on the other hand, are designed primarily for hand-operated control in either direction.
Power driven flexible shafts have two general classes of application--those in which the shaft operates in a given position and the curve, or curves, of the shaft remain substantially fixed; and those in which there is relative movement between the driving and driven elements, and the curvature and twisting of the shaft is continually changing, as when, for example, a driven element such as a portable grinding tool is continuously moved about the workpiece by an operator. In such case, the prior art devices, which coupled the power driven rotating flexible shaft to the spindle of the grinding tool, were rigidly threadedly secured between the flexible shaft and spindle, and hence, were incapable of preventing twisting of the casing of the flexible shaft during grinding operations. Under such operating conditions, certain threaded connections employed in the prior art coupling devices often times loosened, such that the high speed flexible shaft rotating within the casing could cause injury to the operator.
The present invention overcomes the aforementioned deficiencies of the prior art by providing a safeguard coupling device which automatically relieves stresses introduced into the casing by twisting thereof caused by movement of the handpiece and worktool by an operator. Furthermore, even if the present inventive safeguard coupling device should malfunction, power to the handpiece or driven element is substantially instantly removed to lessen any danger of injury to the operator.